In her study, published in the journal Human Biology in February 2011, Fortunato examined evolution patterns of language and marriage customs in 27 Indo-European societies, from Iceland to India, to determine when monogamous marriage became widely practiced.

According to Fortunato, the practice of monogamy is more than 8,000 years old. She attributes one important reason for its rise to the growth of agricultural societies, where a man had to consider how many children would be inheriting, and therefore dividing, his land and wealth.